1. Field of the Invention
The present invention relates to flexible cable assemblies for rotary actuation, as in an automobile speedometer or tachometer cable, or for linear actuation, for example in a push-pull remote control cable. It relates more particularly to an assembly comprising a spiral-cut tubular plastic liner with multiple internal ribs, within a tubular outer housing, the liner and housing together forming a tubular casing for supporting a power-transmitting core member. The ribs on adjacent spiral turns of the liner are offset from one another and support the center core member at spaced locations, resulting in quiet and smooth cable operation. The invention also relates to a method of manufacturing the plastic liner of the cable assembly.
2. Description of the Prior Art
Prior cable assemblies having internal liner structures with spaced supports for the center core member are disclosed in U.S. Pat. Nos. 3,581,523 (Bartholomew), 3,481,156 (DeCsipkes), and 3,240,333 (Johnston). Such constructions are also disclosed in French Pat. No. 1,294,854 (1962) and German Pat. No. 1,045,184 (1959).
The Bartholomew patent discloses a continuous tubular conduit liner having an inside surface provided with ribs extending inwardly from the liner to contact the center core member and resist radial movement. The ribs are integrally formed on the liner and are equally spaced around its inside circumference. The ribs may alternatively comprise a series of short rib sections extending either longitudinally or circumferentially on the liner. The Bartholomew construction is said to exhibit low noise during operation (col. 2, lines 31-32). Nevertheless, a ribbed liner constructed in accordance with Bartholomew provides support only every 60.degree. or 90.degree. about the center core member. This leaves other circumferential sections of the shaft unsupported and therefore subject to radial movement and possible contact with the tubular conduit liner. Such movement can also create noise.
Another potential disadvantage of the Bartholomew liner is that a lubricant disposed between the shaft and the liner may be pumped upward or downward within the liner by the rotation of the shaft. Flexible shafts are commonly formed of multiple layers of wire. The layers are wound so that successive layers have alternating directions of winding or lay about the central wire. The outer screw-like surface of such a shaft can act as a pump, particularly if the interior of the conduit is smooth, or if the shaft and any interior texture of the conduit liner have opposite lays. Thus, if the shaft surface has a left-hand lay (that is, the turns in the shaft surface are oriented from lower-right to upper-left as the shaft is viewed in a vertical position), upward pumping may result if the shaft is rotated clockwise as seen from its lower end, i.e., opposite to the direction of the lay.
Cable assemblies having ribbed sleeve members similar to Bartholomew are disclosed in the above-mentioned DeCsipkes and Johnston patents as well as in the French and German patents. The purpose of these constructions is also said to be the reduction of noise and friction.
U.S. Pat. Nos. 2,382,966 (Ahrens), 2,831,737 (Jacoby) and 3,435,634 (Chatham) disclose further cable type constructions wherein the inner core member is supported by sleeve members having a ribbed or discontinuous inner supporting surface.
The prior art further includes plastic members that are deformed inwardly by the pressure of a helically-wrapped outer structure to form a helical ridge for supporting a center core member. See U.S. Pat. Nos. 3,302,479 (Conrad) and 3,214,995 (Gilmore).
Additionally, the prior art includes helically or spirally wound liner members for supporting an inner core member. Examples of these constructions are disclosed in U.S. Pat. Nos. 3,238,808 (Barnard) and 2,850,915 (Bratz). In Barnard and Bratz the helical or spiral liner is said to improve flexibility, increase lubricant capacity and retention, and reduce noise levels of the assembly.